Mark Sheppard, who is well known to sci-fi fans for roles in Firefly and Battlestar Galactica, told SCI FI Wire that he shot a quick-turnaround guest appearance on SCI FI's upcoming original series Warehouse 13.

"A while back, I got a lovely call from my friends at SCI FI, nine and a half pages of dialogue, to do in a day," Sheppard said in an exclusive interview Wednesday at the Electronic Entertainment Expo in Los Angeles, where he was promoting The Conduit, in which he does a voice. "I was actually out doing publicity for The Conduit on the East Coast. And they called and said, 'Can you go to Toronto to rehearse on Sunday to shoot on Monday?' I'm like, 'I'm in New York. It's not that hard.' So it was perfect."

Mark Sheppard at the High Voltage Software booth at E3

In the show, two Secret Service agents (Eddie McClintock and Joanne Kelly) find themselves abruptly transferred to Warehouse 13, a massive, top-secret storage facility in windswept South Dakota that houses every strange artifact, mysterious relic, fantastical object and supernatural souvenir ever collected by the U.S. government.

Sheppard will guest-star as Mr. Valda, the enigmatic representative of the Regents, the mysterious organization that controls Warehouse 13. He disapproves of Artie's (Saul Rubinek) methods as the team leader of the Warehouse and isn't afraid to let him know it.

Following is an edited version of our interview with Sheppard. Warehouse 13 premieres on July 7 and will air on Tuesdays. The Conduit comes out on June 23. (Possible spoilers ahead!)

You flew to Toronto?

Sheppard: I went up there and got to meet Jack Kenny, the executive producer. Amazing guy. There are really good people up there. I love what he's doing. SCI FI has been great to me. NBC and SCI FI. ... I went up and did several scenes with Saul Rubinek, who is one of my favorite actors, and CCH Pounder. They're just two powerhouse actors. They created a role for me, and I would like to think that the role will come back.

So tell us more about your character.

Sheppard: Well, Warehouse 13 is the repository of all supernatural stuff that has existed through time, and, as I understand it, tends to exist in the dominant superpower's realm. So one time it looked the Nazis were taking over, and it managed to burn itself down and reappeared a little later in America, who seems to have had control of it for a little bit. I've always liked the analogy that it's like the warehouse where they would have put the Ark of the Covenant from Raiders of the Lost Ark. But it's a little cleverer than that. It's funny and witty, and it's got some great acting in it, and I think it's something that could be really exciting for SCI FI. We're dealing with Lewis Carroll's mirror and James Braid's chair. Some interesting stuff there, you know? It's very clever writing and very, very good acting all the way around.

I've been brought in as spokesperson for the Regents, who are the organization who look after the Warehouse. Sort of a Knights Templar for the Warehouse, if you will. It's an interesting position. It will be an interesting time. We shot our scenes in a very strange location for what it is that we were doing. It's going to be very interesting to see how this unfolds.

So where was it?

Sheppard: No, no, no. I'm not going to give that away. That's the good stuff. It was a lot of fun. I'm on Leverage, where Saul Rubinek played the guest in the pilot. I kept crossing paths with him, and never actually meeting him. I'm a huge fan of his. He's a fabulous actor, and he plays the guy who's really in charge, who runs the scene but looks after the Warehouse. It's a really good story. ...

You've worked more than once with Joss Whedon, first in Firefly and now in Dollhouse.

Sheppard: Joss is special. I don't always know what he's doing. I don't always understand what he's doing. I don't know that he always understands what he's doing [laughs]. But he's still brilliant. He's a lot of fun to play with. He likes to mix it up a lot. I play a role in Dollhouse called Agent Tanaka. You want to work out why I'm playing an agent Tanaka as a character in the show?

I was wondering ...

Sheppard: Well, hopefully someday we'll actually explain it to you. If we ever get to it. And he likes to mix stuff up. I mean, I'm such the obvious bad guy when you bring me into something. But he put me in this role where you're never quite sure what I'm going to end up as. It's a lot of fun for me, and I'm sure it makes him giggle a lot. ...

So you're here at E3 promoting the Wii game you do voice work on, The Conduit.

Sheppard: I love these guys [High Voltage Software, the game developers]. These guys are straight up and dead honest. It's the same thing to me. A great storyteller is a great storyteller. They've had 16 years of building other people's games. They go to build their own game, and they decide to make a first-person shooter for the Wii. I mean, how insane has that got to be?

Until you play the game and you go, "Wow, this is the smartest thing I've ever seen. ... They made it for us." I mean, we all have Wiis, so we all want something to play on it. ... But they brought me in real early for this. ... And I'm a gamer, and I love to play, and there's nothing better for me than to go sit in a Conduit booth and say, "Hey, I'll play multiplayer with you guys. I'll play with you all day."